On 1 November 2006 Alexander Litvinenko, ex-KGB officer and by then a British citizen, met two of his former colleagues, Andrei Lugovoi and Dmitri Kovtun, in Mayfair and drank a cup of tea with them. What happened next must count as the century’s most gruesome crime so far. The tea taken by Litvinenko was laced with a dose of polonium-210 and he died in agony in UCH several days later. The radioactive substance was detected on a belated hunch of a brilliant forensic scientist. The suspects, Lugovoi and Kovtun, had already left Britain, and the Metropolitan Police found polonium deposits at nearly every hotel and shop that they had visited.

Litvinenko’s widow Marina told the world that her husband was the victim of an assassination masterminded by none other than President Putin and his FSB. The Home Office at the time was reluctant to disturb diplomatic relations with Russia and withheld cooperation from the inquest led by Judge Robert Owen.

The political situation changed in early 2014, when Putin annexed Crimea and the United Kingdom and other western powers applied economic sanctions. The Home Secretary, Theresa May, announced permission for a public inquiry and brought Owen back from retirement to head it. Over several months the inquiry laboriously took its evidence in open and closed proceedings. Lugovoi and Kovtun obstructed progress by refusing to submit to oral examination.

The inquiry was a multidisciplinary process that tested the wits of everyone present as researchers in disparate arcane fields strove to make their findings intelligible to non-specialists. As someone who gave written and oral evidence, I can testify to the judge’s scrupulousness in helping witnesses through the cross-examination when the questions from the lawyers seemed inappropriate or unhelpful.

In A Very Expensive Poison, the Guardian journalist Luke Harding gives a superb exposition of the cast of people — FSB agents, MI6 informers, international money launderers, atomic scientists, hospital doctors, academics and London police officers — who were involved in the inquiry. As a former Moscow correspondent, he is well-placed to sketch the political and criminal background to the case. He has consistently supported Marina Litvinenko against Putin and campaigned for the need for the UK authorities to handle Russian affairs more robustly.

Owen’s report in January this year caused surprise to those gathered in Court 73, as few had expected him to be so bold as to name Putin as having ‘probably’ been the man who set the criminal enterprise in motion. And what an enterprise it was. The polonium affair had been only the last of several attempts to murder Litvinenko. Working for the wealthy Russian exile Boris Berezovsky, Litvinenko had repeatedly denounced Putin for complicity in a gamut of illegality. In 2005 he even accused him, wildly, of being a pederast. If there was anyone who made himself a target for an FSB operation, it was Litvinenko.

Harding’s account makes one see Lugovoi and Kovtun as the Laurel and Hardy of intelligence work. Their clumsy performance is almost beyond belief. But there is also another way of looking at their behaviour. Could it be that the FSB feels such contempt for its own agents that it failed to tell the pair of them about the chemical nature of the poison? One wonders how much polonium-210 entered their bodies. Lugovoi is nowadays feted in Moscow as a Duma deputy and TV chat-show guest. But surely in the dead of night he must wonder whether he made the right choice of employer.

Robert Owen stressed that he relied on closed evidence when arriving at his conclusions. The problem with this is that he provided no clue as to what he learned from the anonymous witnesses. We are left guessing whether MI6 has a high-placed mole in the Kremlin or GCHQ intercepted electronic communications. Owen offered no explanation for this silence.

The result is that the Russian media have had a merry old time dismissing the inquiry as a stitch-up. On the day of the verdict, the usual London-based suspects criticised the absence of overt corroboration. Soon the Moscow media — and not just the lickspittle TV channels — were making the same point. Meanwhile, David Cameron and Theresa May announced a small number of additional sanctions against a few Russian leaders. Just as the inquiry sprang into life at a moment of tension between Moscow and Westminster, so now the British government aims to avoid annoying Putin while he is offering a degree of co-operation in Syria.

Marina Litvinenko worked with grace and determination to obtain justice for her late husband, and the public inquiry has put several shots at goal past Alexander’s killers. But the suspicion arises that the British judicial system, by its secretiveness, has nudged the ball into the back of its own net.